Production of aromatic hydrocarbons from furans



United States Patent '0 BRODUCTIDN OF AROMATIC HY DROCARBONS EFROM. FURAN S NoDrawing. Application Decembenfl, 195,1, Serial No. 263,684

Claims priority, application Greatiillritain January 17, 1951 .4. Claims. (Cl. --260668) and in which R1, R2, .-R3 and R4 are selected from hydrogen,

-methyl, ethyl, n-propyl and-isopropyLsaid derivative-containing-at least-six carbon atoms, in the vapourphase,---and at:aiemperaturewitlrinsthe range f 3.00 10 1750' .C. with 'aioatalyst,rasehereinafter:defined.

Catalysts suitable for use in the processiofiuthe. present invention are those normallyemployed in aromatisation reactions. .Those comprising metals of group VIII .ofthe periodic system, and the oxides of ,chromium,.molybdenum .and vanadium are particularly suitable. Ihesetmaybe .employedin conjunction with metallic oxides, sufclifas alumina ,andmagnesia. "Preferred catalysts are .chromic oxide-alumina, rand supportedrplatinum ca,talysts such2 as platinum on charcoal.

A chromic oxide-alumina catalyst may be produced by dehydrating alumina trihydrate, AlzOaSHaO, at a temperatureof-400 C. until the product contains from 9 to 1'l-%-"by weight of water. The product is pelleted using a suitable pelletinglubricant,subsequentlyheatedif-necessary at a temperatureof 700 .C. .to .removethis lubricant "if its presence is-undesirable and'the pell-ets are zithen :soaked ina' solutionof chromicacid' until .theyacquire-the desiredchromium'content. They are then driedat an elevated temperature of, for example, 400 C. The chromiumoxidescontent of the final catalyst is preferably 10 to: hy-weight. *Itis also-advantageous to incorporate -.a'tminoramount of magnesiumchromate' intothe catalyst-s; a suitable amount is 2% by weight, expressed "as the percentage --'by weight of MgOin the final catalyst.

The reaction is carried out by contact-ingthehydrogenated furan derivative with the catalyst maintained at an elevate'd temperature =within the range 013300 to 750 C. The optimum temperature depends upon the catalyst employed; :inparticular, when the catalyst comprises chromic oxideealumina, the temperature employed is pref- .erably'inthe region'of 500 "C.

The process-of the I present invention 1 is preferably carried out "by -continuous=operation. "The vaporised *furan derivative is preferably contacted with the cat'alyst at a ice space velocity :within the range of 0.01 to"1- litre.o'fliquid -furancompoundper. hour. .per litre of catalyst-filled space.

The process. maybe carried" out in the presenceof a carrier gas'such as nitrogen or hydrogen. This may be ac iciteidffor examplahy passing a stream of hydrogen through theneaction -vesseltogether Withthe vaporized hydrQgenate'd .furan derivative.

According toan important-embodiment of the present invention, xylene hydrocarbons, andmore-particularly paraatylene, 'are'xproduced :by contacting 2,2,5.',5 -tetramethyl tetrahydrofuranor .2,2,'5,'5 -.tetramethy1 2,5 -di-hydro- .furan, r;or.'*-a-mixture 1thereof, 'with a catalyst, as; hereinbeforedcfined, at atemperature within the range of 300 t 75.0 13y operating inttbisimanner; hig'hpassyiclds of para-xylenemay be .obtained.

hn vmrkingiin .thcpresence-of: added .hydrogem using 2,2,5,;5. .tetr.amet-h-Yl 2,-5-dihydrofuran as .=the starting material,;- should be {-znoted. that in "the reactor-thisv maye'ebe hydrogenatedwgto 2,2,5;S-tetramethyltetrahydrofnran prior to the production-ofxylenes. The present invention therefore .covers the direct conversion of 2,2,5g5etetramethyl 2 ,5.-dihydrofuran to :paraxylene :and :the- .convers'ionnwhen it takes place via the formationrof '2,2,;5.;5:1tetramethyl tetrahydrofuran as an intermediate.

"."Inthe process of the present invention, aliphatichydrocarbons maybe 'pro'duced'in appreciable amounts. These may be recycled to'the catalyst zone, whereby they mayipe largely converted to aromatichydrocanbons. fIJiu s, when .2.5., m hY i2; =d hydroiuran. a con ac ed with a chnomic oxide-alumina catalyst, maintained ata tempfillature of '500C.,"the product contained dimethallyl, 1,1- 4;4-tetrarnethylbutadiene, 2,5=dimethylhexane and 2*,5-di- :methylhexenes, Einadditionto the main product which -was para'exylene. "In-an importantembodimentof the process of the present invention, aliphatic hydrocarbons, produced as described above,,are .recycledto the catalyst zone together with a further portion ofhydrogenated furan derivative. In this manner, they may be largely converted toparaxylene.

'The"2;2,5,5 tetramethyl 2,5-dihydro'furan' or 2,25,5- tetramethyltetrahydrofuran or mixtures" thereof foruse in the present invention may be produced by any convenient method. It is an important featureof the present inventionthatthe initial startingmaterialfor their production is 2;5-'dimethylhex-3 yne'- 2,-5-diol, which may be;pr'oduced by condensingacetone with acetylene in the presence'of potassium hydroxide ora potassium alkoxide. This ;yne-

diol may be hydrogenated to 2,5-dimethylhex-3 end-25- diol-or 2,5-dimethylhexane 2,S-diol, era-mixture thereof. 'The diol-containing product may then be dehydratedto '2,2, '5;;5-.tetramethyl 2,5-dihydrofuran or 2,2,5 ,5 -tetrame thyl tetrahydro'furan or a mixture thereof. Suitable dehydrating agents are phosphoric acid, sulphuric acid, hydrochloric acid, zinc chloride, acetic anhydride, preferably containi-ng a small amountof sulfuric acid, ;and -p-tolnene sulphuric-acid. 'Ihus,;the diol may' be contacted with phosphoric acid containing in thcregion of 60% by weight of HaPOr'ata temperature of, for example, 100 C. When usinghydrochloric acid, a normal solution of this issuit- "a'bfle,'-and"on reacting this-With the'diol atSO" C., a

, water-insoluble upper layer is producedin thereaction product, and this comprises substantially pure 2, 35,5- tetramethyl"2;5 dihydrofuran and/or 2 ;2,'5,'-5- tetramethyl tetrahydrofuran.

EXAMPLE 1 *A-mixture containing 55.9 grams of '2,5-dimethy1hex-3- ene-2,5'-'dio'l' and 15.7 grams of 2,5-dimethylhexane.-2,5- dio'l was heated with -65'0-mls. of phosphoric acid, con- 'taining 56%**by weight H3P04. A mixture of 2,2,15,5- tetramethyldihydrofuran and 2,2,5,i tetramethyltetrahydrofuran;Weighing-57.2 grams,-was obtained.

41.4 grams of this mixture were fractionated; the following fractions were obtained:

The 2,2,5 ,S-tetramethyl-Z,S-dihydrofuran prepared; in this example had n =1.4039 and n ==1.4064.

75.1 grams of 2,2,5,5-tetramethyl 2,5-dihydrofuran,-produced by the process described above, were passed at a rate of 22.5 mls./hour over 375 mls. of a chromic oxidealumina catalyst maintained at a temperature of 500 C. The chromic oxide-alumina catalyst contained 13% by weight of chromium oxides, 85% by weight of activated alumina, and 2% by weight of magnesium oxide, present as magnesium chromate. Hydrogen was passed through the reaction zone at a rate of 3 litres/hour.

63.6 grams of liquid product were obtained. This, on analysis by fractional distillation and infra-red investigation, was found to contain: 7

Thus, the total pass yield of aromatic hydrocarbons was 50%, and these aromatics contained 98% by weight of p-xylene. The total pass yield of aliphatic hydrocarbons containing the carbon skeleton:

-( 3-cc( :-0 o C was in the region of 36%. Since these aliphatic hydrocarbons may be recycled, and thus converted in good yield to p-xylene, the total yield of p-xylene can exceed 80%.

EXAMPLE 2 I 59 grams of 2,5-dirnethylhexane-2,5-diol were distilled with 580 mls. of phosphoric acid containing 60% by weight H3PO4.2 ,2,5,5-tetramethyl tetrahydrofuran and water distilled over. The water was returned to the distillation flask to maintain the phosphoric acid concentration at a constant value. 47.4 grams of crude 2,2,5,5- tetramethyl tetrahydrofuran were obtained, and on fractionation, 44.3 grams of pure 2,2,5,5-tetramethyl-tetrahydrofuran were isolated, corresponding to a yield of The 2,2,5 ,S-tetramethyl tetrahydrofuran obtained in the process contained 74.8% by weight carbon, and 12.6% hydrogen. These figures are in close agreement with the theoretical values of 75.0 and 12.5% respectively. The sample had a boiling point of 112 C., and n 3 =1.4015. These properties are not in agreement with those hitherto reported in the literature, but the sample had a Raman spectrum which was in complete accordance with it being 2 ,2,5,5-tetramethyl tetrahydrofuran. r 40.2 grams of 2,2,5 ,5-tetramethyl tetrahydrofuran (boiling point 112 C.; n =1.4015) were passed over 100 mls. of $43" pellets of a chromic oxide on alumina catalyst, comprising 13% by weight of oxides of chromium, 2% by Weight of magnesia (present as magnesium chromate) and 85% by weight of alumina. The reaction was carried out using a liquid space velocity of 0.1 litre of feed per hour per litre of catalyst-filled space. The operating temperature was 550 C., and 5 litres of hydrogen were passed per hour through the reaction zone.

The product from this reaction comprised 4.5 litres of "gas (apart from hydrogen fed), 4 grams of water, and

25.8 grams of organic liquid. 0n distillation, this gave the following fractions:

Fraction 1. 532 3%. 35%;

1 96-106 3. 0 2 s 106-139 8. 6 3 139 10. 6 Residue a 3. 6

Fraction 3 was found to be substantially pure para-xylene.

These fractions were analysed by the application of the infra-red technique. The table below summarises the results obtained.

A. Aromatic hydrocarbons identified bltercenltit bPercersr}:1 t P t y weig y weig ercen Product of total of total ass liquid aromatic Yield product product 1 0. 3 2 0. 8 3 0. 8 6 2. 4 44 11. 4 88 34. 2 Toluene 2 0. 5 4 1. 7

B. Ali hatic hydrocarbons identi ed Percent Percent by weight by weight Pass Product of total $5 5 5559;; Yield, liquid mafia percent product product Dimethallyl 3. 5 0. 9 7. 0 2. 6 1,1,4,4-Tetrameth y l b u t a diene 5 1. 3 10. 3 3. 8 2,5-Dimethylhexane 6 1. 55 12. 3 4. 2 Unidentified material 35 8. 9 70. 0

Infra-red analysis indicated that the unidentified material had a carbon structure of the type present in 2,5-dimethyl hexane.

EXAMPLE 3 Pass Weight,

yield. grams percent Toluene 0. 3 1 Dimethallyl 1. 7 6 p-Xylnnn 7. 65 2s 1,1,4,4-tetramethylbutadiene 13. 2 46 2,5-dimethylhexane 2,5-dimethylhexenes 4. 45 15 Thus, 67% of the mixture fed to the reaction zone is converted to aliphatic hydrocarbons which may be recycled to the conversion zone, and converted in high yields .to aromatic hydrocarbons. The conversion of the starting material to other products is 33 of these other products, 84% is para-xylene.

We claim:

1. A process for the production of hydrocarbon mixtures comprising para-xylene which comprises the step of contacting at least one hydrogenated furan derivative selected from 2,2,5,5-tetramethyl-2,5-dihydrofuran and 2,2,5,S-tetramethyltetrahydrofuran in the vapour phase and at a temperature within the range of 300 to 750 C. with a catalyst consisting essentially of an effective amount of chromic oxide and alumina.

2. A process for the production of hydrocarbon mixtures comprising para-xylene which comprises the step of contacting at least one hydrogenated furan derivative selected from 2,2,5,5-tetramethyl-2,5-dihydrofuran and 2,2,5,S-tetramethyltetrahydrofuran in the vapour phase and at a temperature within the range of 300 to 750 C. with a catalyst consisting essentially of an effective amount of platinum supported on charcoal.

3. A process for production of hydrocarbon mixtures comprising para-xylene which comprises the step of contacting 2,2,5,S-tetramethyl-Z,S-dihydrofuran in the vapour phase and at a temperature within the range of 300 to 750 C. with a catalyst consisting essentially of an effective amount of chromic oxide and alumina.

4. A process for the production of hydrocarbon mixtures comprising p-xylene which comprises the step of contacting at least one hydrogenated furan derivative selected from the group consisting of 2,2,5,5-tetramethyl-2,5-dihydrofuran and 2,2,5,5-tetramethyltetrahydrofuran in the References Cited in the file of this patent UNITED STATES PATENTS 2,157,365 Vaughn May 9, 1939 2,241,792 Reppe et al. May 13, 1941 2,250,445 Bruson et al July 29, 1941 2,273,484 Guinot Feb. 17, 1942 2,302,345 Pesta et a1. Nov. 17, 1942 2,310,809 Reppet et a1. Feb. 9, 1943 OTHER REFERENCES Slobo'din et al.: Chem. Abst., 43 (1949), col. 1017-8 (1 page only). 

1. A PROCESS FOR THE PRODUCTION OF HYDROCARBON MIXTURES COMPRISING PARA-XYLENE WHICH COMPRISES THE STEP OF CONTACTING AT LEAST ONE HYDROGENATED FURAN DERIVATIVE SELECTED FROM 2,2,5,5-TETRAMETHYL-2,5-DIHYDROFURAN AND 2,2,5,5-TETRAMETHYLTETRAHYDROFURAN IN THE VAPOR PHASE AND AT A TEMPERATURE WITHIN THE RANGE OF 300* TO 750* C. WITH A CATALYST CONSISTING ESSENTIALLY OF AN EFFECTIVE AMOUNT OF CHROMIC OXIDE AND ALUMINA. 